Abstract:

The object of research is stress analysis of worn chisel. The interaction between soil particles and chisel leads to change of shape and dimension of a worn chisel or other agriculture tools. The wear rate depends on the velocity of the chisel in the soil, position in the soil and shape of a chisel. These factors change the dimension and shape of chisel during its service life. The modern chisel includes sintered carbides on a tip. Sintered carbides plates are effective protection for wear resistance. But the body of the chisel is not protected and its wear resistance is lower than the tip. The service life of the tip is much higher than the body of the chisel. Stresses of the body of the chisel are stationary during the service life. The aim of this study is determining of optimising process of the strength of steel for chisels.

Abstract:

Chisels and tines for agricultural machinery are mechanically worn. Mechanical wear depends on the microstructure of the material. The desired microstructure of the material, specifically steel is obtained by heat treatment. Microstructure after heat treatment can be determined in two ways. The first one is the experimental determination, which is timeconsuming and not economically efficient. The second is to build the thermal model during the heat treatment. Microstructure is affected during the heat flux during heat treatment. This research was focused on the boundary conditions of the model heat flux during quenching. The heat flux was measured during quenching with solid cylindrical samples (ø25–50 mm) by means of two thermocouples. The first temperature was measured in the axis of the sample and the second temperature was measured near the sample surface. The results of the heat flux were appointed to the model and experimentally verified. In this way it is possible to construct a model of tines and chisels for agricultural machine, which shows the progress of the heat flux during quenching.

Abstract:

Quenching as a heat treatment method is commonly used to control the mechanical properties of steels. This article deals with the modelling and simulation of quenching of steel chisel using a multi–phase model. The process of the heat treatment is non stationary phase due to temperature variation with time. In this study, the problem of heat transfer in three dimensional phase was transformed into a two dimensional axisymmetric case. ElmerFem solver was used for the heat transfer through different cooling media such as water, oil and salt bath. The results from heat solver were used for austenite transformation modelling by applying Johnson–Mehl–Avrami–Kolmogorov equation in TTT diagram. The Scheill’s decomposition was used for anisothermal transformation of austenite. The hardness prediction was done according to simple mixture rule where total hardness of the steel was calculated based on volume of the phases and their Vickers hardness.